|National Seasonal Rainfall Outlook: probabilities for Spring 2006, issued 23rd August 2006|
Mixed spring rainfall outlook
The spring (Sep-Nov) rainfall outlook shows a mixed pattern of odds, with below average totals more likely in northern Australia and a few patches in the southeast, while the chances favour wetter than average conditions in southwest WA, the Bureau of Meteorology announced today.
The pattern of seasonal rainfall odds across Australia is a result of higher than average temperatures in both the Pacific and Indian Oceans, the latter of which has been warming strongly in recent months.
For the September to November period, the chances of above median rainfall are below 40% over much of the NT, most of northern and western Queensland, and in parts of southern Victoria and northern Tasmania (see map). In Queensland, the chances drop below 35% and approach 25% in the Northern Goldfields district.
So in years with ocean patterns like the current, about six or seven springs out of ten are expected to be drier than average in these various parts of Australia, with about three or four out of ten being wetter.
In contrast, part of southwest WA has a 60 to 65% chance for the spring rainfall total to exceed the long-term median. This equates to six springs being wetter than average and four drier for every ten years with ocean temperatures similar to the present.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During spring, history shows this effect to be moderately consistent across most of the eastern mainland states and the NT, as well as northern Tasmania, southwest and far northwest WA, and parts of SA (see background information).
The Southern Oscillation Index (SOI) was negative for the third straight month in July with a value of −9. This came after readings of −6 in June and −10 in May. The approximate SOI for the 30 days ending 20th August was −16. If history is any guide, the SOI will probably stay negative for the rest of the year.
Although a late-developing El Niño event is still a possibility this year, especially considering the SOI, the consensus from computer models is for continued neutral ENSO conditions for the remainder of 2006, but on the warm side of average. Continued Pacific warmth and negative SOI values are generally associated with increased likelihood of below average rainfall in eastern and northern Australia. For routine updates and comprehensive discussion on the latest data relating to ENSO, together with details on what the phenomenon is and how it has affected Australia in the past, please see the ENSO Wrap-Up.
Click on the map above for a larger version of the map. Use the reload/refresh button to ensure the latest forecast map is displayed.
|The following climate meteorologists in the National Climate Centre can be contacted about this outlook: Grant Beard on (03) 9669 4527, Andrew Watkins on (03) 9669 4360, Lynette Bettio on (03) 9669 4165.|
Regional commentary is available from the Climate and Consultancy Sections in the Bureau's Regional Offices:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 26th SEPTEMBER 2006